The model layer

The model layer of our application will contain the following:

• The Question structure, responsible for holding the question string, as well as the expected answer (true/false)
• The QuestionController class, responsible for loading the questions as well as advancing to the next question:

// Question.swift
enum BooleanAnswer: String {
    case `true`
    case `false`
}

struct Question {
    let question: String
    let answer: BooleanAnswer
}

extension Question {
    func isGoodAnswer(result: String?) -> Bool {
       return result == answer.rawValue
    }
}

// QuestionController.swift
class QuestionController {
    private var questions = [Question]()

    // Load the questions from memory or disk
    func load() { /* load from disk, memory or else */ }

    // Get the next question, if available
    func next() -> Question? {
        return questions.popLast()
    }
}

As you notice, we have implemented our model with a controller, which helps us to perform complex logic at the model layer such as loading the questions from the network or from a local database.

The QuestionController can also be subclassed to accommodate one's needs with regard to specific questions to be loaded, different difficulty levels, and so on.